基于外部DEM的InSAR图像配准方法研究

雷达图像的配准是进行雷达干涉测量(SAR Interferometry, InSAR)处理的关键,为了保证干涉相位图或形变相位图反映真实地面特性,需要雷达图像之间亚像元级精度的配准。首先综述了已有的基于外部DEM的InSAR图像配准方法的思路及其不足之处,并提出了一种全新的思路:以图像之间的相干性作为目标函数,利用搜索的方法实现了雷达成像方位向和距离向的最优时间常数的估计,从而实现雷达图像之间亚像元级配准;还进一步推导了数字高程模型(Digital Elevation Model, DEM)的误差对算法精度影响的一个更加严密的表示。结论表明,在利用精确轨道数据的情况下,美国航天飞机测地计划SRTM获得的地形数据的精度可以满足精确雷达图像配准的要求。结果表明,利用基于外部DEM算法配准雷达图像在山区和大的时间基线情况下要优于常规相干多项式配准方法,理论上可以达到百分之一个像素的配准精度。     

快速区域互相关InSAR图像配准方法

在分析复图像干涉相位对快速互相关算法配准精度影响的基础上,提出了一种快速区域互相关InSAR图像配准方法。该方法对图像的幅度谱进行区域相关操作,获得干涉相位空间角频率的粗估计,并对主图像进行干涉相位补偿。该算法通过上述步骤消除干涉相位变化对算法的影响实现了高精度配准。在仿真实验和实测实验中,通过与传统的快速区域互相关算法及最大频谱法进行对比,验证了本文算法的稳健性与有效性。     

基于光流法的迭代反投影超分辨率重构算法

为了提高重构图像或者视频的分辨率．提出把新型的基于光流法的图像配准算法应用于迭代反投影（IBP）超分辨率算法中。在所提出的方法中．基于光流法的图像配准算法用来提高图像配准的准确性。首先,为了得到像素级别的运动矢量．基于光流法的图像配准算法被用于估计图像间的运动矢量。以得到更加准确的运动矢量矩阵。接着,利用所获得的运动矢量矩阵结合迭代反投影算法重构高分辨率的图像。同时．由于基于光流法的图像配准能够很好地估计视频图像间的运动．所提出的方法同样适用于视频图像的超分辨。实验结果表明．提出的方法对于图像或者视频的超分辨率效果．在主观效果和客观评价上都有一定的提升。     

基于信号子空间估计的多基线InSAR干涉相位图滤波方法

多基线干涉合成孔径雷达（Interferometic synthetic aperture radar,InSAR）利用长短基线之间的关系,能够获得优于单基线InSAR的高程测量结果。本文针对多基线InSAR的数据特点,提出了基于信号子空间估计的多基线InSAR干涉相位图滤波方法。该方法将不同长度基线下所获得干涉相位图中同一像素单元信号作为一个训练样本,通过信号子空间的估计完成多基线InSAR干涉相位图滤波。仿真实验结果表明,本文方法可以在运算时间相当的情况下,获得优于回转均值滤波算法和回转中值滤波算法的滤波性能,是一种可满足实时处理要求的有效的多基线InSAR干涉相位图滤波方法。     

融合SIFT特征的熵图估计医学图像非刚性配准

配准准确性是医学图像配准算法的一项重要指标,像素灰度是目前图像配准中广泛使用的特征,但是灰度特征来源单一,而且忽略空间信息,在一些情况下容易产生误配。针对这个问题,本文提出一种融合SIFT特征的熵图估计医学图像非刚性配准算法。该算法首先使用基于互信息的刚性配准算法对两幅待配准图像进行粗配;然后,在采样点上提取像素灰度和SIFT高维特征,并在此基础上构造k-最邻近图(kNNG);最后,使用k-最邻近图来估计α互信息(αMI)。实验结果表明:和传统的基于互信息和像素灰度的刚性配准算法,基于熵图估计和单一像素灰度特征的非刚性配准算法相比,本文提出的算法具有更高的配准准确性。     

一种改进的病理显微图像亚像素快速配准方法

针对病理显微图像的快速高精度配准的应用需求,提出了一种改进的亚像素快速配准方法。通过采用对数差值函数对显微图像重叠区域进行信息量评估,由H型对数差值模板配准获取两幅图像像素级的粗定位和有效子图,继而在两幅子图上采用局部上采样相位相关法来获取亚像素级别的配准估计值。该方法利用H型对数差值模板简洁、配准速度快的优点规避了相位相关法计算量随着图像尺寸增大而急剧增长的缺陷,并能够对显微图像进行信息量评估以避免空白图像造成的误配。经实验表明,改进的显微图像配准方法配准精度可达0.01像素,速度为相位相关法的3.7倍（图像大小为2448×2048）,更适合应用于病理显微图像的快速高精度配准。     

局部相位相关用于图像亚像素级配准技术研究

提出了一种基于局部相位相关的高效和鲁棒的亚像素级图像配准方法。通过传统的相位相关算法估计出初始平移参数后,在初始位置的引导下对互相关功率谱进行上采样矩阵Fourier变换,实现了图像局部相位相关,得到图像间亚像素级平移参数。实验结果表明,算法配准精度较高,且对随机噪声和光照变化具有较强的鲁棒性。     

雷达干涉条纹图滤波方法研究

在合成孔径雷达干涉测量中,为滤除干涉图像中存在的各种噪声,提高相位解缠结果及生成的数字高程模型的精度.从分析干涉条纹图的特点入手,对干涉条纹图的圆周期中值滤波法进行了研究,提出一种基于高斯噪声估计的自适应圆周期中值滤波方法,给出了算法设计及详细的实验数据并与其它滤波方法进行比较.试验结果表明,该方法可以较好地消除干涉图像中存在的噪声,而且保留更多的图像边缘、细节信息.     

混合基线InSAR构形下的SAR-GMTI方法研究

文中提出一种基于坡度补偿的联合像素杂波抑制方法,为了消除混合基线InSAR构形下由于垂直基线引入的地形起伏干涉相位的影响,该方法利用坡度补偿技术使杂波局部满足独立同分布,并且利用杂波子空间和噪声子空间的正交性来抑制静止杂波,同时能够充分利用当前像素和周围像素的信息,因此对配准误差具有很好的稳健性.仿真和实测数据的处理结果证明了该方法的有效性.     

基于光流法运动配准的覆冰图像超分辨率重建

针对电力监控系统中输电线路易晃动造成覆冰图像模糊,提出基于光流法运动配准的覆冰图像超分辨率重建算法。该算法首先利用基于光流法的图像配准算法估计图像间的亚像素级运动矢量,得到前向和后向配准图像;然后,利用迭代反投影(IBP)算法对估计出的图像分别进行超分辨率重建;最后,根据配准误差加权得到最终的输出图像。实验结果表明,相对于传统算法,该算法的重建结果无论是在峰值信噪比和标准差还是基于对比敏感度的无参考图像清晰度上,均有明显提高,具有较好的客观指标和视觉效果。     

An estimation method for InSAR interferometric phase combined with image auto-coregistration

1 Introduction Synthetic aperture radar interferometry (InSAR) is an important remote sensing tech- nique to retrieve the terrain digital elevation model (DEM)[1,2]. Image coregistration and interferometric phase unwrapping are two key processing procedur…     

SAR-GMTI investigation in hybrid along- and cross-track baseline InSAR

A joint-pixel clutter suppression method based on slope compensation is proposed in this paper. In order to eliminate the effect of the terrain interferometric phase caused by the cross-track baseline in hybrid baseline InSAR, the local independent identical distribution of the clutter is satisfied by using the slope compensation technique, and thus the clutter can be suppressed successfully by using the orthogonality of the clutter subspace and the noise subspace. This approach utilizes the information contained in the current pixel as well as in its neighbors, showing robustness to the image coregistration errors. Both the simulated data and the real airborne data are used in proving the validity of the presented approach. Supported in part by the National Nature Science Foundation of China (Grant No. 60802074) and the Program for New Century Excellent Talents in University     

Joint interferometric calibration based on block adjustment for an airborne dual-antenna InSAR system

Mapping large areas using airborne dual-antenna interferometric synthetic aperture radar (InSAR) usually requires processing and mosaicking of different scenes from multiple strips. The overlapping areas of these multiple strips should have consistent elevation values. Due to the unstable attitude of the plane, the interferometric parameters usually vary for each scene during mapping. Therefore, interferometric calibration technology for high-precision height retrieval is required for the correction of the interferometric errors. The traditional interferometric calibration methods for a single scene usually use ground control points (GCPs) to estimate the interferometric parameters – this method cannot guarantee a consistent height in the area of overlap. Besides, GCPs are difficult to deploy over rough terrain, making it impossible to use traditional calibration methods. In this article, a joint interferometric calibration method based on the block adjustment theory used in photogrammetry is proposed for airborne dual-antenna InSAR. This method considers the accurate digital elevation model (DEM) height reconstruction model and can be applied with sparse GCPs. The principle of the proposed method is to make the best use of the GCPs within all the scenes and the tie points (TPs) between the adjacent scenes to establish an error relationship model. First, the weighting values of all GCPs and TPs based on their retrieval elevation error caused by the interferometric phase error and the position distribution difference are introduced in the proposed method. Next, the interferometric parameters are weighted to reduce the condition number of the normal equation. Then, an alternative approximation approach combined with the sparse matrix decomposition technique LDL^T is utilized to solve the normal equation, and the corrected interferometric parameters for each scene are obtained. High-precision joint interferometric calibration results for airborne InSAR systems are achieved by the proposed method and validated by experiment. Using the proposed method, the average mean error (AME) and root mean square error (RMSE) are below 0.6037 and 0.9176 m, respectively. Meanwhile, the maximum AME and RMSE of the reconstructed DEM height difference for the validation TPs in the overlapped area of the adjacent scenes are reduced from 1.2909 and 1.7245 m to 0.8864 and 1.2087 m, respectively.     

优化的区域增长InSAR相位解缠算法

在区域增长的干涉合成孔径雷达（InSAR）相位解缠算法中,种子的选择和种子相位值的确定是之一.本文研究了优化的区域增长2维相位解缠方法,包括合适的种子选取和种子相位值的优化处理,提出了将干涉相位图中相位跳变导致的边缘曲线作为种子,通过分析边缘曲线之间的相邻关系,基于遗传算法优化种子的相位值.仿真结果表明,该算法的计算量与干涉相位图的像素点数成近似线性关系,同时由于该算法属于局部算法,可以通过并行处理进一步提高计算效率.优化的区域增长2维相位解缠算法与其他2维相位解缠算法相比较,其解缠后的相位条纹与原始干涉相位图相位条纹的一致性非常好.该算法的处理结果与最小成本网络流相位解缠法相当,但其计算量却远远小于最小成本网络流相位解缠法的计算量.     

Forest canopy height and carbon estimation at Monks Wood National Nature Reserve, UK, using dual-wavelength SAR interferometry

Forest canopy height is a critical parameter in better quantifying the terrestrial carbon cycle. It can be used to estimate aboveground biomass and carbon pools stored in the vegetation, and predict timber yield for forest management. Polarimetric SAR interferometry (PolInSAR) uses polarimetric separation of scattering phase centers derived from interferometry to estimate canopy height. A limitation of PolInSAR is that it relies on sufficient scattering phase center separation at each pixel to be able to derive accurate forest canopy height estimates. The effect of wavelength-dependent penetration depth into the canopy is known to be strong, and could potentially lead to a better height separation than relying on polarization combinations at one wavelength alone. Here we present a new method for canopy height mapping using dual-wavelength SAR interferometry (InSAR) at X- and L-band. The method is based on the scattering phase center separation at different wavelengths. It involves the generation of a smoothed interpolated terrain elevation model underneath the forest canopy from repeat-pass L-band InSAR data. The terrain model is then used to remove the terrain component from the single-pass X-band interferometric surface height to estimate forest canopy height. The ability of L-band to map terrain height under vegetation relies on sufficient spatial heterogeneity of the density of scattering elements that scatter L-band electromagnetic waves within each resolution cell. The method is demonstrated with airborne X-band VV polarized single-pass and L-band HH polarized repeat-pass SAR interferometry using data acquired by the E-SAR sensor over Monks Wood National Nature Reserve, UK. This is one of the first radar studies of a semi-natural deciduous woodland that exhibits considerable spatial heterogeneity of vegetation type and density. The canopy height model is validated using airborne imaging LIDAR data acquired by the Environment Agency. The rmse of the LIDAR canopy height estimates compared to theodolite data is 2.15 m (relative error 17.6%). The rmse of the dual-wavelength InSAR-derived canopy height model compared to LIDAR is 3.49 m (relative error 28.5%). From the canopy height maps carbon pools are estimated using allometric equations. The results are compared to a field survey of carbon pools and rmse values are presented. The dual-wavelength InSAR method could potentially be delivered from a spaceborne constellation similar to the TerraSAR system.     

Efficient mitigation of atmospheric phase effects in repeat-pass InSAR measurements

The problem of atmospheric phase effects is currently one of the most important limiting factors for widespread application of repeat-pass interferometric synthetic aperture radar (InSAR) measurements. Due to the extraordinary complexity of the atmospheric inhomogeneity and turbulence, it is generally difficult to obtain satisfactory mitigation of the atmospheric phase effects in repeat-pass InSAR measurements. In recent years, several methods have been developed for mitigating the atmospheric phase effects. An effective approach is interferogram stacking, which is based on stacking independent interferograms. However, as many as 2n images are required to generate n interferograms and the atmospheric delay errors of the stacked interferogram decrease only with the square root of the number of interferograms in the conventional interferogram stacking method, which is not very efficient. In order to efficiently mitigate the atmospheric phase effects on the stacked interferogram in repeat-pass InSAR measurements, we propose a relay-interferogram stacking method. Compared with the conventional method, this method not only can efficiently mitigate atmospheric phase effects on the stacked interferogram, but also greatly decreases the number of required synthetic aperture radar (SAR) images. The key element is that the first and the last SAR images are selected from the periods of similar meteorological conditions. In addition, we present an application of the approach to the study of ground subsidence in the area around Beijing, China.     

基于随机并行梯度下降算法的InSAR相位解缠方法

相位解缠是干涉合成孔径雷达InSAR数据处理中的一个关键步骤,解缠结果的好坏直接影响最终数字高程模型的精度。介绍了一种基于随机并行梯度下降SPGD算法的解缠方法,该方法对图像中各相位点施加随机并行扰动,通过迭代使得解缠误差代价函数收敛到全局最优值,从而实现相位解缠的目的。模拟和实测数据实验结果表明,相较于最小二乘解缠方法,随机并行梯度下降解缠算法精度更高,且原理简单,易于实现,为相位解缠提供了一个全新的思路。     

A wavelet domain detail compensation filtering technique for InSAR interferograms

The quality of interferogram filtering affects the accuracy of interferometric synthetic aperture radar (InSAR) applications. This article presents a new wavelet domain filtering method for phase noise reduction in an InSAR interferogram. The method first transforms the real and imagery parts of the original interferogram into the wavelet domain using the stationary wavelet transform (SWT). Then the coefficients for each sub-band are filtered with detail compensation. Finally, the wavelet coefficients are reconstructed in the space domain by the inverse SWT. The results show that the proposed method can suppress the speckle effectively, maintain details of the interferogram well, and greatly reduce the number of residues.